New general synthesis of tetrahydro‐1,2,4,5‐tetrazin‐3(2 H )‐one derivatives and stable 3,4‐dihydro‐3‐oxo‐1,2,4,5‐tetrazin‐1(2 H )‐yl radical derivatives

Reactions of 2‐chloroformylhydrazones of aromatic aldehydes or ketones 2 with various hydrazines were converted to monocarbonohydrazone derivatives 3 or 5 and/or tetrahydro‐1,2,4,5‐tetrazin‐3(2 H )‐one derivatives 6 , 7 . By oxidation with lead dioxide, compounds 6 were transformed into stable 3,4‐dihydro‐3‐oxo‐1,2,4,5‐tetrazin‐1(2 H )‐yl radical derivatives 8 .